The present invention relates to a charged particle beam exposure apparatus, or more in particular to a charged particle beam exposure apparatus utilizing a blanking aperture array (BAA).
In recent years, semiconductor technology has advanced and the integrity and the function of the semiconductor integrated circuits (IC) have improved to such an extent that the technology in this field is expected to play the central role in the technological development of the whole computer, communication and machine control industries. There is a general trend that the density of ICs increases by about four times every three years. The storage capacity of the dynamic random access memory (DRAM), for example, has increased from 4M to 16M to 64M to 256M and to 1 G. This ever-increasing integration of the LSI depends to a large measure on advances in micromachining technology in the semiconductor manufacturing process.
Under the circumstances, the limit of micromachining technology is defined by the pattern exposure technique. As a technique for exposing a pattern, an optical exposure apparatus called a stepper is currently used. In an optical exposure apparatus, the minimum width of the pattern that can be formed is defined by the wavelength of an exposure light source due to diffraction. A light source which outputs ultraviolet light is currently used, and it has become increasingly difficult to use the light of a shorter wavelength. For achieving a finer micromachining technology, a new exposure method other than the optical exposure apparatus has been under study.
The charged particle beam exposure is known as a means which can realize the micromachining of not more than 0.05 .mu.m with a positioning accuracy of not more than 0.02 .mu.m. In the prior art, however, the charged particle beam exposure has been considered difficult to use for mass production of LSIs because of its low throughput as compared with the stepper.
The throughput problem now encountered in the charged particle beam exposure is a result of using single-stroke electron beam exposures to produce continuous scans by a single particle beam (electron beam), for example, but it is not the result of a sincere study, based on the analysis of the probable cause of the physical and technological bottlenecks, to improve the throughput. Specifically, the prevailing judgment that the charged particle beam exposure cannot be used for mass production of LSIs due to a low throughput is nothing but a consideration from the viewpoint of productivity of the apparatuses now available on the market.
On the other hand, an application of the block exposure or the multi-beam exposure using the blanking aperture array (BAA) has recently reached the stage where a charged particle beam exposure apparatus having a throughput of about 1 cm2/sec may be realized. Especially, the multi-beam exposure using the BAA, though somewhat inferior in accuracy to the block exposure, has the advantage that exposure of a high throughput is possible regardless of the shape and density of a pattern. This invention relates to a charged particle exposure apparatus of a multi-beam type using the BAA. In the description that follows, the charged particle beam exposure apparatus of multi-beam type using the BAA will be sometimes referred to simply as the BAA exposure apparatus. A detailed configuration of the BAA exposure apparatus is disclosed in U.S. Pat. No. 5,260,579, etc.
For the plotting speed to be increased for the BAA exposure apparatus, the BAA driving speed for on/off control of the beams is required to be increased. For this purpose, it is necessary to increase the transmission rate in the signal transmission path from the BAA control circuit to each blanking electrode of BAA. The signal transmission path from the BAA control circuit to each blanking electrode of BAA has an open terminal, and therefore substantially no current flows in the transmission path. For this reason, in the signal transmission path for applying the voltage signal output from the BAA control circuit to each blanking electrode, the voltage signal is transmitted without regard to the impedance. Further, the signal transmission path from the BAA control circuit to the blanking electrodes is considerably long. In the conventional transmission path, therefore, the signal cannot be easily transmitted at high speed, and the BAA driving speed is limited by the transmission rate in the signal transmission path. For increasing the BAA drive speed, therefore, the transmission rate is required to be increased in the signal transmission path from the BAA control circuit to each blanking electrode.
An electron beam is radiated from an electron gun to the BAA board. The electron beam is a flow of high-voltage (the voltage of the electron gun) charge, and the signal transmission path to each blanking electrode is charged to high voltage by the electron beam radiated. The current generated by the radiation of the electron beam is as minute as several .mu.A, while the voltage sometimes assumes a value as high as several tens of KV. As long as a voltage is applied by the driver of the BAA drive circuit to the signal transmission path, therefore, the particular voltage is maintained. In the case where the driver is turned off or the signal transmission path is open midway and no driver is connected, on the other hand, the signal transmission path increases to so high a voltage that the charge moves (migrates) transiently between the signal transmission paths proximate to each other or between a signal transmission path and a DC-level power line connected to a common electrode, thereby often developing a dielectric breakdown in a short time. The apparatuses currently in use have a circuit board in the signal transmission path from the driver to the blanking electrodes, and the signal transmission paths approach each other most closely in the circuit board. Therefore, a board resistant to the migration is used, constituting one of the causes of an increased cost.
Further, when the signal transmission path increases in voltage as a result of electron beam radiation, the driver is supplied with a high voltage, often posing the problem of the breakdown of the driver. A similar phenomenon occurs in the case where the signal transmission path which is open due to the insufficient contact of the connector or the like is reconnected.
As described above, the BAA charged particle beam exposure apparatus with BAA arranged in the path of the charged particle (electron) beam has the problem that the radiation of a charged particle beam on the BAA applies a high voltage to the signal transmission path leading to the apertures of the BAA, thereby breaking the signal transmission path and the driver.
With the electron beam exposure apparatus of BAA type, it is absolutely necessary that individual apertures operate accurately to secure an accurate exposure pattern. In view of the fact that a connection board and a probe card are arranged in the route from the board carrying the BAA drive circuit to the BAA board and these boards are connected by connectors or a cable, however, the signal transmission path is liable to open, leading to a considerably high failure rate. Further, there are as many signal transmission paths as BAA apertures in the signal transmission path leading from the board carrying the BAA drive circuit to the BAA board. The defect probability of the great number of signal transmission paths is multiplied by the number of the channels thereof. For improving the utilization rate of the apparatus, therefore, it is critical to check regularly whether a defect has occurred or not and to pinpoint a defective portion and repair any defect that has occurred.
A conceivable method of detecting a defect consists in detecting the voltage signal of the electrodes or the electrode pads of the BAA board directly. Since the BAA board is contained in a vacuum apparatus, however, it has hitherto been very difficult to detect the voltage signal by direct contact with the electrodes or the like. Especially during the exposure operation, the electrodes of the BAA board cannot be directly contacted. For detecting the occurrence of a defect in this method, therefore, the apparatus is required to be stopped provisionally at the sacrifice of a very low operating efficiency. Further, the measurement by direct contact with the electrodes has an effect of producing a state different from the state during the exposure, and therefore cannot be conducted accurately.
A method for detecting the electrode voltage without directly contacting the electrode is by using an electron beam probe. Since the BAA is so minute, however, direct detection with the electron beam probe has been difficult. This method also requires that the apparatus be stopped temporarily.
To overcome this problem, a probe having an electrode is arranged in place of a specimen, each electron beam is turned on selectively to detect the current flowing in the probe, and a beam with a different current amount is detected to detect a defective signal transmission path. This conventional method, however, involves so small a current amount per beam that a defective transmission path cannot be identified with sufficiently high accuracy.
For the reason described above, the actual practice of discovering a defective point has been to contact each point of the signal transmission path physically using a measuring instrument to check the conductive state. However, this has been a very troublesome job because of the great number of signal transmission paths.
In spite of a high probability of defect occurrence due to the long and multiplicity of signal transmission paths to the apertures of the BAA, the discovery of the occurrence of a defect and pinpointing a defective point has been difficult, especially during the exposure operation.